Exploring the effect of Brønsted acidity of MFI-type zeolites on catalytic cracking temperature of low density polyethylene

Abstract

Catalytic cracking of plastics using zeolites is a means of promoting the recycling of petrochemical resources. However, the detailed effects of the zeolite Brønsted acidity (acid strength, acid amount, location of acid sites, etc.) on the catalytic cracking of plastics have remained unclear. We synthesized MFI-type zeolites with different acid strengths and amounts and compared their low-density polyethylene cracking temperatures with each other. We also aimed to provide guidelines for future catalyst design. Zeolites with controlled acidities were synthesized by introducing different amounts of trivalent metals (Al, Fe, and Ga). The results confirmed that the higher the acid strength and the amount of acid in the zeolites, the lower the cracking temperature of the plastic. However, the cracking temperatures reached a plateau as the amount of acid increased, and the degree of the plateau depended on the acid strength. The acid strength is more important than the acid amount for the cracking temperatures. In addition, we investigated the effect of the location of the acid sites using MFI-type zeolites with different external surface areas and core–shell MFI-type zeolites coated with silicalite-1 as inert shell layers. It was also found that both the acid sites on the outer surface and those within the zeolitic pores were effective in catalytic cracking.